Wow, that's kind of tough. My quick thoughts:
1. Not taking Zim would mean only one pitcher for your keepers (then again, you were going to keep A-rod so you're must OK with that).
2. Molina is a top-3/top-5 catcher who probably bats in the middle of the lineup, as are your other top three hitters, so that's very nice start to your lineup. He's also a top-50 player as a catcher across most sites I've checked, so I don't see how you can let him go.
3. I really like Zimmerman, but he did have that late slide last season, otherwise he's be a slam dunk.
4. Not keeping Rios would mean no OFs...hmmmm.
Definitely keep Molina. If you go Zimmerman, you have a solid core of infield hitters and can probably round out the OF while still keeping two SPs. If you go Rios, you should take a look at the likely player pool and make sure there'll be a couple of SPs worth picking up for your #2 and #3 SP.
I think I'd keep both Zim and Molina and drop Rios.